1. Field of the Invention
This invention relates to a thermosensitive recording material, and more particulary to a thermosensitive recording material utilizing a coloring reaction between a leuco dye and a color developer capable of inducing color formation in the leuco dye upon application of heat thereto.
2. Discussion of Background
Recently, various information recording materials of a non-enviromental-pollution type, capable of nursing resources and economizing energy, have been developed and put to practical use for the purpose of dealing with a great variety of abundant information. In particular, thermosensitive recording materials have been widely employed in various fields, for instance, for use with terminal printers for computers and calculators, recorders for medical measurement instruments, low- and high-speed facsimile apparatus, automatic ticket vending apparatus, copying machines, and label printing machines for the POS system, because of the following advatages thereof:
(1) images can be readily recorded on a thermosensitive recording material by simply applying heat thereto without employing a complicated development process;
(2) a relatively simple and small-sized apparatus is available for preparing a thermosensitive recording material, handling of the recording material is easy, and the maintenance cost of the same is inexpensive; and
(3) in the case where paper, which is not costly as compared with other materials, is used as a support, a thermosensitive recording material with the plain paper-like touch is obtainable.
In general, the thermosensitive recording material is prepared by coating a liquid for forming a thermosensitive coloring layer, which contains a coloring component capable of inducing color formation upon application of heat thereto, onto the surface of paper, synthetic paper or a plastic film, and then dried. Images are recorded on the recording material thus prepared by a thermal pen or a thermal head.
The thermosensitive recording materials have the above-desribed advantages, and yet they are disadvantageous in that they readily develop color when they are pressed or heated by friction. Such color development brings about fogging, and the image quality is thus drastically deteriorated.
In particular, thermosensitive recording materials having high sensitivity are now being developed aiming at reducing the amount of electric power consumed by a facsimile apparatus, a printer or the like, and prolonging the life span of the thermal head. Owing to the high sensitivity, these recording materials develop color more easily than the conventional ones when they are pressed or heated frictionally.
In order to improve the above problem, a specific material having color-fading characteristics has been incorporated into a thermosensitive recording material as disclosed in Japanese Patent Publications 57-59078, 57-18517 and 60-21552. This material can fade color once developed in the recording material. The recording material containing such a material, however, cannot be preserved for a prolonged period of time.
Japanese Patent Publication 50-14531 discloses a thermosensitive recording material containing a wax by which the recording material can be protected from developing color by scratching. This recording material, however, cannot sufficiently withstand frictional pressure, and is poor in matching characteristics.
A non-aqueous alkylphosphate compound has been proposed in Japanese Laid-Open Patent Application 62-149478. It is however unfavorable to incorporate this compound into a thermosensitive recording material having extremely high sensitivity, which has been developed so as to fulfill rescent various demands, for example, for high-speed printing. This is because if a coloring agent having extremely high sensitivity exists in a thermosensitive layer together with the non-aqueous alkylphosphate compound, the coloring agent develops color before the alkylphosphate compound reveals its effect.